1. Field of the Invention
The present invention relates to a positioning device and a method of initializing a positioning device, preferably, to be used for semiconductor exposure devices, various kinds of machine tools, various kinds of precision measuring devices, and the like.
2. Description of the Related Art
FIG. 17 is a view illustrating a wafer stage 100 for a semiconductor exposure device (not shown) as an example of the prior art. FIG. 18 is a view illustrating part of the construction shown in FIG. 17, for ease of understanding.
As shown in FIG. 18, wafer stage 100 includes a stage surface plate 1, an X beam 2, a Y beam 4 and an XY slider 13 (see FIG. 17). The X beam 2, the Y beam 4 and the XY slider 13 are movably guided on the stage surface plate 1 by means of gas bearings (not shown), respectively The X beam 2 is movably guided along a side face of an X yaw guide 3 in a direction X by means of gas bearings (not shown). Similarly, the Y beam 4 is movably guided along a side face of a yaw guide 5 in a direction Y by means of gas bearings (not shown).
The X beam 2 and the Y beam 4 are provided at each of their both ends with a coarse linear motor moving part using permanent magnets. FIG. 17 shows that sets of X coarse linear motor stationary parts 8 and Y coarse linear motor stationary parts 9 are also provided in such a manner as to embrace the respective coarse linear motor moving parts from above and below. The coarse linear motor stationary parts 8 and 9 each comprise iron cores made of laminated silicon steel plates arranged in the form of comb teeth, and coils wound around the teeth. Although a magnetic attraction force may be exerted between the iron cores and the coarse linear motor moving parts, this magnetic attraction force is canceled by the arrangement of the stationary parts 8 and 9, embracing the moving parts with the same clearances from above and below. By suitably causing current to flow through the coils of the coarse linear motor stationary parts 8 and 9, a thrust force can be generated between the coarse linear motor stationary parts 8 and 9 and the coarse linear motor moving parts.
Positions of the X beam 2 and the Y beam 4 in their moving directions are measured by means of laser interferometers 83 and 84. The X beam 2 and the Y beam 4 are provided with corner cube reflecting surfaces (not shown), which reflect laser beams or radiation beams X1, X2, Y1 and Y2 irradiated from the laser interferometers 83 and 84. The X beam 2 and the Y beam 4 are positioned by driving and controlling the coarse linear motors on the basis of the values measured by the respective laser interferometers 83 and 84.
The XY slider 13 (FIG. 17) has an upper plate 15 (FIG. 18) and a bottom plate 14 (FIG. 18) and is arranged in such a manner as to surround the coarse motion X beam 2 and the Y beam 4. The self-weight of the XY slider 13 is supported by the stage surface plate 1 through gas bearings (not shown) provided on the bottom plate 14. Gas bearings 18 are provided between the XY slider 13 and the X and Y beams 2 and 4. The XY slider 13 is movably guided by the X beam 2 in the direction X and by the Y beam 4 in the direction Y, as a result of which, the XY slider 13 is moved in both the directions X and Y. FIG. 18 illustrates the stage with the X beam 2, the Y beam 4 and the upper plate 15 shifted in the direction Z (i.e., in the vertical direction).
Provided on the upper plate 15 (FIG. 18) are fine linear motors and a fine movement stage 16 (FIG. 17) through a self-weight supporting portion. The self-weight supporting portion includes gas bearings and magnets so that the fine movement stage 16 is insulated from vibration which would otherwise be transmitted thereto. The fine linear motor includes a linear motor stationary part provided on the XY slider 13 and a linear motor moving part provided on the fine movement stage 16. A single phase coil is provided as the linear motor stationary part, and a permanent magnet is provided as the linear motor moving part. The fine movement stage 16 is movable relative to the XY slider in the directions X, Y and Z, and directions ωx, ωy and θz, which are rotational directions about the axes X, Y and Z, by means of the fine linear motors.
The fine movement stage 16 is provided with a mirror having a reflecting surface (not shown). Positions (displacement) of the fine movement stage 16 having six freedoms of movement can be measured by reflecting a laser beam or a radiation beam at the reflecting surface of the stage 16 from a laser interferometer (not shown). The fine movement stage 16 is positioned by driving and controlling the fine linear motor on the basis of values measured by the respective laser interferometers.
In a case in which positions of an object are measured by the use of the laser interferometers, as described above, there is a need to initialize (to calibrate) positional data of the laser interferometers. This is because the interferometer measures relative positions of an object, but not absolute positions.
In general, the initialization may be carried out when turning on a power source. In a commonly-used method for initializing positional data, an object is moved to a reference position, whereupon the measured value is changed to a desired value. In this case, for example, a mechanical abutment or a shading switch may be used as a reference position.
In an initialization sequence, it is required to move an object to the reference position. The coarse linear motors may be operated in a system that selects polyphase coils to be energized. Methods for selecting coils to be energized are disclosed in Japanese Patent Application Laid-Open Nos. 64,487/1993 and 316,607/1999.
In order to move an object to a reference position, moreover, the object must be guided. In a case in which the XY slider 13, the X beam 2 and the Y beam 4 are guided with the aid of gas bearings, as described above, the guiding function can be given to the gas bearings by supplying gas to them when turning on the power source. In a case in which the XY slider 13, the X beam 2 and the Y beam 4 are guided by the use of electro-magnetic guidance, however, there is no guiding function when turning on the power source.